1. Field of the Invention
The present invention relates to medical devices and, in particular, to methods and devices of preventing restenosis.
2. Description of the Related Art
Many causes of restenosis in angioplasty have been theorized among health care professionals. Many diseases cause body lumens to undergo stenosis or a narrowing of a canal within the body. The resulting reduced blood flow can permanently damage tissue and organs. Stenotic regions that limit or obstruct coronary blood flow are a major cause of ischemic heart disease related mortality.
The therapeutic alternatives generally used for treatment of stenosis involve intervention (alone or in combination of therapeutic agents) to remove the blockage, replacement of the blocked segment with a new segment of artery, or the use of catheter-mounted devices such as a balloon catheter to dilate the artery. The dilation of an artery with a balloon catheter is called percutaneous transluminal angioplasty (PTA). A stent may also be delivered, as known in the art.
Often angioplasty permanently opens previously occluded blood vessels; however, restenosis thrombosis, or vessel collapse may occur following angioplasty. A major difficulty with PTA is the problem of post-angioplasty closure of the vessel, both immediately after PTA (acute reocclusion) and in the long term (restenosis).
Re-narrowing (restenosis) of an artery after angioplasty occurs in 10-50% of patients undergoing this procedure and subsequently requires either further angioplasty or other procedures. Restenosis (chronic reclosure) after angioplasty is a more gradual process than acute reocclusion: 30% of patients with subtotal lesions and 50% of patients with chronic total lesions will go on to restenosis after angioplasty. Because 30-50% of patients undergoing PTCA will experience restenosis, restenosis has limited the success of PTCA as a therapeutic approach to coronary artery disease.
Recently, intravascular stents have been the focus of substantial attention as a means of preventing acute reclosure after PTA. Most stents are delivered to the desired implantation site percutaneously via a catheter or similar transluminal device. Once at the treatment site, the compressed stent is expanded to fit within or expand the lumen of the passageway. Stents are typically either self-expanding or are expanded by inflating a balloon that is positioned inside the compressed stent at the end of the catheter. Intravascular stents are often deployed after coronary angioplasty procedures to reduce complications, such as the collapse of arterial lining, associated with the procedure.
However, stents do not entirely reduce the occurrence of thrombotic abrupt closure due to clotting; stents with rough surfaces exposed to blood flow may actually increase thrombosis, and restenosis may still occur because tissue may grow through and around the stent and the lattice of the stent.